u-blox, the company selling GPS module, indeed less than $10, releases a utility application named "u-center" and through its application we can configure output frequency of "PPS" terminal up to 10 MHz.

During the GPS status like above (getting enough information for positioning, but I don't use position information), time domain and spectrum are measured for several frequency range.

The first one is 1 MHz spectrum. Please note it is 10 kHz span (one horizontal division is 1 kHz). VERY CLEAN!

Accordingly, time time domain waveform is also clean, naturally.

Let's try 4MHz. YES it is still clean!

Yeah, it is clean pulse. Please note that, the connection is not 50 Ohm line but just breadboard jumper and we may get more clear signal with shielded and impedance controlled situation.

This is 8MHz, still clean, very clean. We can drive ATmega328 with Arduino bootloader with this signal now.

Yes, it has a clean manner! Enough clean to drive MCU!

Now let's try 10MHz. Indeed 10 MHz is a commercial standard signal (any time domain related measurement instrument has 10 MHz in/out.), and if we can easily get 10 MHz, it should be quite useful,, but as you see, surely 10 MHz is the maximum spectrum frequency but it is not pure one at all. In the datasheet of u-blox Neo6, this "bad spectrum" is due to the way to generate signal. The original frequency is 48 MHz and the signal is generated by internal "bad" PLL. It seems, the frequency divided by integer seems clear spectrum and waveform...

The result of 12 MHz. The spectrum again get very clean. Yes, 12=48/4.

As noted above, if we use impedance controlled careful signal line from GPS module to oscilloscope it may have more clear waveform...

Now let's try 16MHz. 16 is 48/3 but not so clear (but clear than 10MHz case).

It has a glitch in time domain waveform. Through appropriate filter we may use this for MCU clock but this time I will use 8 MHz signal for MCU driving. (Indeed this is out of spec in the datasheet).